In a typical injection molding machine one or more pairs of A and B mold bases (the letters A and B refer to the usually fixed and usually movable bases, respectively) is mounted, respectively, on the top clamp plate and base support plate of the machine. Plural A and B mold inserts usually having mold cavity defining means therein are fixed in the bases in paired alignment, whereby upon closure of the base support plate toward the top clamp plate respective pairs of oppositely disposed mold inserts are brought together to close the mold cavities. Molding material is fed through the top clamp plate and A mold base thereon to a runner distribution system in the two mold bases, and molding material is delivered from such distribution system to respective mold cavities to mold parts. Moreover, an ejector apparatus usualy is provided to eject the molded parts from the opened mold cavities and the sprue from the runner distribution system by means of ejector pins that extend, for example, through the base support plate, B mold base and B mold inserts mounted thereon.
Some disadvantages to such conventional injection molding systems are the lengthy time required for set-up, long down-time required for repair, and minimum versatility. For example, it often takes half a day or more for a skilled worker to mount mold inserts accurately in respective mold bases. Usually, though, there is some initial misalignment which is discernible only after the mold bases are used in the injection molding machine; whereupon the mold bases are removed from the machine for fine adjustment alignment of the mold inserts therein using shims, spacers and other conventional means. Such removal too, is difficult due to the heavy weight of the assembled mold bases and mold inserts.
If a part becomes stuck in a mold cavity or runner distribution system and cannot be removed easily, the entire mold base often is removed from the injection molding machine to remove the stuck part, thus causing substantial down-time of the machine.
To avoid the need to realign mold inserts in a mold base after having been aligned accurately already, the mold inserts often are kept in the mold base for use in subsequent production of injection molded parts. Such retention of assembled mold inserts and bases results in high inventory costs. Also, to replace a defective mold insert with a functional one in an already aligned set-up of mold inserts in a mold base, to add a mold insert to such an already aligned set-up, etc. is time consuming with attendant high labor cost.